Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $112.32   12.144%   $125.9601   $125.96   $125.95   $126.00  
  Purchase #2 $244.37   10.540%   $270.1266   $270.13   $270.15   $270.10  
  Purchase #3 $148.70   13.758%   $169.1581   $169.16   $169.15   $169.20  
  Purchase #4 $226.70   11.436%   $252.6254   $252.63   $252.65   $252.60  
  Purchase #5 $242.45   6.841%   $259.036   $259.04   $259.05   $259.00  
  Purchase #6 $42.32   7.169%   $45.3539   $45.35   $45.35   $45.40  
  Purchase #7 $122.81   8.756%   $133.5632   $133.56   $133.55   $133.60  
  7 purchase totals = $1,139.67       $1,255.8233   $1,255.83   $1,255.85   $1,255.90